Internal combustion engines have a cylinder block and at least one cylinder head which are connected to one another at their assembly end sides so as to form the individual cylinders, that is to say the combustion chambers.
To hold the pistons or the cylinder liners, the cylinder block has a corresponding number of cylinder bores. The pistons are guided in the cylinder liners in an axially movable fashion and form, together with the cylinder liners and the cylinder head, the combustion chambers of the internal combustion engine.
The cylinder head often also serves to hold the valve drive. To control the charge exchange, an internal combustion engine requires control elements and actuating devices for actuating said control elements. During the charge exchange, the combustion gases are discharged via the outlet openings, and the charging with fresh mixture or fresh air takes place via the inlet openings. To control the charge exchange, in four-stroke engines, use is made almost exclusively of lifting valves as control elements, which lifting valves perform an oscillating lifting movement during the operation of the internal combustion engine and which lifting valves open and close the inlet openings and outlet openings in this way. The valve actuating mechanism required for the movement of the valves, including the valves themselves, is referred to as the valve drive.
It is the object of the valve drive to open and close the inlet and outlet openings of the cylinders at the correct times, with a fast opening of the greatest possible flow cross sections being sought in order to keep the throttling losses in the inflowing and outflowing gas flows low and in order to ensure the best possible charging of the combustion chamber, and an effective discharge of the exhaust gases. Combustion chambers are also increasingly provided with two or more inlet openings and outlet openings.
The intake lines which lead to the inlet openings, and the exhaust lines which adjoin the outlet openings, may be at least partially integrated in the cylinder head. If two or more outlet openings are provided per cylinder, the exhaust lines of each cylinder are often merged—within the cylinder head—to form a partial exhaust line which is associated with the cylinder, before the partial exhaust lines are merged. The merging of the exhaust lines is referred to generally, and within the context of this disclosure, as an exhaust manifold or manifold.
Downstream in the exhaust-gas discharge system, the exhaust gases are then, if appropriate, supplied to the turbine of an exhaust-gas turbocharger and/or to one or more exhaust-gas aftertreatment systems.
In the case of exhaust-gas-turbocharged internal combustion engines, it is sought to arrange the turbine as close as possible to the outlet of the internal combustion engine in order thereby to be able to make optimum use of the exhaust-gas enthalpy of the hot exhaust gases, which is determined significantly by the exhaust-gas pressure and the exhaust-gas temperature, and to ensure a fast response behavior of the turbocharger, since in order to improve the response behavior, the exhaust-gas volume in the exhaust lines upstream of the turbine should be as small as possible.
Secondly, the path of the hot exhaust gases to the different exhaust-gas aftertreatment systems should also be as short as possible such that the exhaust gases are given little time to cool down and the exhaust-gas aftertreatment systems reach their operating temperature or light-off temperature as quickly as possible, in particular after a cold start of the internal combustion engine.
In this connection, it is therefore fundamentally sought to minimize the thermal inertia of the part of the exhaust line between the outlet opening at the cylinder and the exhaust-gas aftertreatment system or between the outlet opening at the cylinder and the turbine, which can be achieved by reducing the mass and the length of said part. The latter also reduces the surface area, which is acted on with exhaust gas, of the exhaust-gas discharge system upstream of the exhaust-gas aftertreatment system or upstream of the turbine, and therefore reduces the heat transfer.
With regard to the use of a turbocharger, it is sought to keep the pressure loss in the exhaust-gas flow as low as possible up to the inlet into the turbine, which may be achieved by way of suitable flow guidance and by a shortening of the exhaust lines or exhaust-gas paths.
To achieve the above-stated aims, the exhaust lines of the cylinders may be merged within the cylinder head so as to form a coherent integrated exhaust manifold, that is to say the exhaust manifold is integrated entirely in the cylinder head. Such a cylinder head is distinguished by a very compact design, with it being possible for the total length of the exhaust lines of the exhaust manifold and the volume of the exhaust lines upstream of a turbine arranged in the exhaust-gas discharge system, or of an exhaust-gas aftertreatment system arranged in the exhaust-gas discharge system, to be minimized.
The internal combustion engine to which the disclosure relates likewise has at least one such cylinder head, in which the exhaust lines of the at least two cylinders merge within the cylinder head so as to form an integrated exhaust manifold.
The integration of the exhaust manifold into the cylinder head furthermore permits dense packaging of the drive unit as a whole, and furthermore has the advantage that said exhaust manifold can benefit from a liquid-type cooling arrangement possibly provided in the cylinder head, in such a way that the manifold does not need to be manufactured from materials which can be subjected to high thermal load and which are thus expensive.
The use of such a cylinder head also leads to a reduced number of components, and consequently to a reduction in costs, in particular assembly and procurement costs.
The way in which the exhaust lines of the cylinders are merged in the specific situation, that is to say the design configuration of the exhaust manifold, is also dependent on the characteristic map areas or objectives for which the operating behavior of the internal combustion engine is to be optimized. Here, the exhaust-gas aftertreatment concept used, and a supercharging concept that may be provided, have a significant influence on the configuration of the manifold and on the exhaust line system connected thereto.
The dynamic wave phenomena occurring in the exhaust-gas discharge system in particular during the charge exchange must be taken into consideration.
In the case of supercharged internal combustion engines in which at least one turbine of an exhaust-gas turbocharger is provided in the exhaust-gas discharge system, impulse supercharging or ram supercharging may be desired.
It may be advantageous for the exhaust gas to be supplied for exhaust-gas aftertreatment immediately after passing through the turbine of an exhaust-gas turbocharger in order to realize or ensure a high conversion rate. In this respect, an exhaust-gas aftertreatment system may directly adjoin the turbine.
Such an arrangement is however hindered by the restricted space availability in the engine bay or on the cylinder head, and by a development trend toward large-volume exhaust-gas aftertreatment systems. The latter also arises from the fact that sufficiently large volumes are required to adhere to the ever more restrictive limit values for pollutant emissions. The volume of the exhaust-gas aftertreatment system has an influence on the residence time of the exhaust gas in the aftertreatment system and therefore on the conversion of the pollutants, that is to say the conversion rate.
Furthermore, use is increasingly made of combined exhaust-gas aftertreatment systems which comprise, that is to say combine, different catalytic converters and/or filters. Oxidation catalytic converters, nitrogen oxide storage catalytic converters, selective catalytic converters and/or particle filters are therefore combined to form integral exhaust-gas aftertreatment systems, as a result of which the volume of the aftertreatment systems is increased. Larger-dimensioned exhaust-gas aftertreatment systems, however, require more installation space, which opposes dense packaging and the most advantageous possible, that is to say close-coupled, arrangement.
The various demands of the different engine concepts generally require very different cylinder heads, or similar cylinder heads but with different integrated exhaust manifolds.
In one example, the issues described above may be addressed by an internal combustion engine having at least one cylinder head, comprising: at least two cylinders, each cylinder having at least one outlet opening for the discharge of the exhaust gases from the cylinder via an exhaust-gas discharge system, each outlet opening being adjoined by an exhaust line, and the exhaust lines of the at least two cylinders merging within the cylinder head so as to form a coherent integrated exhaust manifold, wherein the integrated exhaust manifold has at least two exhaust extraction lines which emerge from the cylinder head, where one exhaust extraction line of the at least two exhaust extraction lines is permanently blocked and has no passages coupled to it, downstream of the one exhaust extraction line.
In this way, the integrated exhaust manifold may be standardized and used in a variety of different engine systems. A standardization of the cylinder head used in engine systems would reduce costs, in particular because the cylinder head constitutes an expensive component of the internal combustion engine. A standardized cylinder head could be manufactured in large unit quantities and used, in accordance with the modular principle, with different engine concepts or internal combustion engines.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.